Generally speaking, when one is interacting with a computer or computer terminal, instructions and data are input through a keyboard by the operator. Inputs can also be delivered, concurrently or not, by automatic readers, sensors, other computers and other kinds of machines and devices, but the human operator interface with the computer is by keystroke in a great majority of cases, aided in some special situations by a "mouse", lightpen or screen touch. This is not surprising because keystroke is the most efficient input for many situations. It provides a quick and relatively simple translation from human language and thought into either machine language or an intermediate code from which machine language can readily be derived by an assembler
Disregarding the limited and special circumstances in which a lightpen, mouse or the like can be used, there are some disadvantages to the keyboard as an input device, especially as an exclusive input device in some situations. Among these are the rather obvious fact that a keyboard occupies the operator's hands, minimizing or eliminating their concurrent use for any other task. Use of the keyboard also requires some degree of training and familiarity with the key location and sequencing as well as some degree of manual dexterity, the necessary amount of skill, training and dexterity being functions of the task to be performed.
Exclusive use of the keyboard as an input device is particularly disadvantageous if the operator must sort through or refer to other documents or the like while interacting with the terminal. Additionally, it would be highly advantageous if an individual in a decision-making capacity could interact with the computer without dealing with the keyboard problem. Still further, certain forms of handicap make the keyboard an obstacle rather than a tool.
While direct voice input to processing machines has been considered and experimented with, it is often regarded as an impractical alternative to keystroke and as somewhat of a technical curiosity. Thus, while the technological capability exists, it is not used.